The Lithiation Reactivity and Selectivity of Differentially Branched Alkyldiphenylphosphine Oxides – A Simple and Versatile Approach to ortho‐Functionalized Arylphosphine Oxides

Alkyldiphenylphosphine oxides typically undergo α‐deprotonation with alkyllithium reagents. Here, the lithiation of differentially branched alkyldiphenylphosphine oxides was investigated and a diverse, but predictable reactivity was found. γ‐Branched derivatives undergo selective directed ortho‐metalation (DoM) using butyllithium and TMEDA as an additive. With decreasing degree of γ‐branching α‐lithiation becomes predominant. The ortho‐phosphinoyllithium intermediates are subject to functionalization and C C bond forming reactions, thus providing a convenient approach to new phosphine oxides and phosphine‐borane complexes, which have a good potential for an approach to new ligands for catalysis.

     

Acylierung von Heterocyclen mit Kohlensäurederivaten. I. Kinetik und Mechanismus der Reaktion von 2-Aminobenzimidazolen mit Arylcyanaten

Acylation of Heterocycles with Carbonic Acid Derivatives. I. Kinetics and Mechanism of the Reaction of 2-Aminobenzimidazoles with Aryl Cyanates The second order rate constants for the reaction of 2-amino-benzimidazoles (2-ABI) with aryl cyanates forming 2-amino-benzimidazole aryl ester imide 3 have been determined in dependence on substituent effects by u. v. measurements. The results are interpreted by a six-membered cyclic transition state in which the electrophilic attack of the cyanate on the endocyclic N atom is catalyzed by an H bridge interaction of the exocyclic amino group of 2-ABI with the OCN group.     

Auswirkungen von Baggerungen und Verklappungen hochwasserbedingter Feinsedimentablagerungen am Fallbeispiel Winterhafen Linz/Donau

In the case study “Winterhafen Linz” the effects of dredging/excavating fine sediments previously deposited by flood events and their subsequent dumping into the Danube mainstream were investigated. While this maintenance work was in progress, the temporal and spatial extent of the sediment plume and the changes in bed topography were measured. By employing air-lift samplers and grab samplers in the dredging and dumping areas, the question as to whether, and if so to what extent, the benthic invertebrate community was disturbed by the maintenance work. It could be clearly demonstrated that the sediment dredging severely affected the benthic invertebrates (an 82 % decline in biomass), while the dumping of the material had no effects on the Danube biota. Numerical modeling was used to simulate discharges and dumping locations other than those actually encountered during the monitoring campaign, thus making it possible to extrapolate and draw conclusions beyond the concrete results. These findings in turn provided the basis for recommendations on how to optimize dredging and dumping procedures on the Danube in future.     

Studies of a thermomechanically treated Al-Zn-Mg alloy

The influence of subgrain structure on the precipitation process in an Al-4.2 wt% Zn-1.6 wt% Mg alloy was studied and correlated with its mechanical properties for ageing temperatures of 110, 142 and 165° C.     

Comparison of methods for determination of microbial biomass in wastewater

Microbial biomass in wastewater was determined by methods used in environmental microbiology and by a method used in wastewater engineering based on a conceptual model simulating fundamental microbial processes in wastewater from measured oxygen uptake rates. The methods originating from environmental microbiology are based on staining and counting of cells for the determination of total cell biomass (acridine orange and DAPI), physiological state of cells (LIVE/DEAD BacLight) and activity of cells (reduction of the redox dye CTC and microautoradiography). Depending on the staining method applied, cell biomasses yielded 15-86% of the biomass defined by the model, and good correlations between cell biomass and model biomass were found. Cell biomass, oxygen uptake and acetate uptake were measured in wastewater, where acetate was added. Substrate uptake rates were found not to be proportional to the increases in cell biomass, suggesting that only a small fraction of the cell biomass was responsible for the main part of the substrate uptake. Despite the differences found between cell biomass and model biomass, it was recommended to use the conceptual model as an engineering tool for simulation of microbial processes and wastewater quality changes. However, there should be a clear distinction between the terms 'model biomass', 'cell biomass' and different activity measurements of cells.     

Method of Calculating the Charge Acceptance of Organic Photoconductors

The charge acceptance of organic photoconductors (OPC) consisting of thin layers must attain the correct value in order to produce constant copy quality. In practice, however, it can be kept constant only by taking elaborate precautions, since a number of parameters have an adverse effect on charge acceptance. The limits are described within which the photoconductors and corona properties fluctuate in actual running machines. The properties of the photo-conductor can scarcely be influenced by the user, but proper choice of the electric parameters of the charging scorotron can largely suppress the influence of the fluctuations on the final charge of the photo-conductor. If the charging device exhibits the behavior of an ideal constant voltage supply characteristic, charge acceptance would depend solely on the tolerances of this device. If the charging device supplies constant current, charge acceptance depends primarily on the properties of the photoconductor. A careful estimate must be made to determine, under conditions as practical as possible, reasons for variations in charge acceptance. There are those caused by fluctuations in the charging device and those caused by fluctuations in the photoconductor. A mathematical method is described which makes it relatively simple to determine the actual OPC charge acceptance depending on application and variation of the electrical parameters.     

Resource management model and performance evaluation for satellite communications

Efficient resource management is mandatory to achieve maximum system capacity for next generation communications systems. Resource management deals with the available spectral band, time, power, and space for a transmission signal. It includes (i) the frequency planning, (ii) the selection of transmit power, and (iii) the assignment of the channels and access nodes to the users. The paper presents a generalized notation as well as graph algorithms for resource management problems. Impairment graphs can be used for frequency planning, whereas flow graphs are suitable for channel access problems. To evaluate the performance of the resource management, service criteria (such as blocking or the carrier to interference ratio C/I) or efficiency criteria (bandwidth requirements) can be derived from the graphs. The resource management techniques are applied to satellite networks with non‐geostationary orbits yielding time‐variant network topologies. As a simple example, the channel assignment and capacity optimization of the EuroSky Way system are shown. Furthermore, a comparison of fixed, dynamic and hybrid channel allocation schemes (FCA, DCA, HCA) for a typical MEO satellite scenario is given. Satellite diversity and its impact on bandwidth requirement and transmission quality is also examined. Finally, it is shown how spread spectrum systems can be investigated with the presented tools. Copyright © 2001 John Wiley & Sons, Ltd.